The present invention relates to roll assemblies which can be used in calenders and analogous machines to treat running tapes, strips or webs or discrete panels or sheets of flexible material, e.g., running paper webs or the like. More particularly, the invention relates to improvements in roll assemblies of the type wherein at least one roll of a pair of rolls which define between themselves a nip for the passage of a web or sheet of flexible material has a deformable shell and contains one or more rows of preferably hydrostatic supporting elements which are displaceable by discrete motors or groups of motors to change the shape of the adjacent portions of the shell.
Roll assemblies of the above outlined character are disclosed in numerous U.S. Letters Patents of the assignee as well as in British Pat. No. 10 58 934. The deformable shell of one of the rolls surrounds a rigid carrier whose end portions are fixedly mounted in the frame of the machine and which supports spaced-apart bearings for the end portions of the deformable shell. The intermediate portion of the shell surrounds a plurality of hydrostatic supporting elements which are displaceable by fluid operated motors, and such motors are adjustable by a control system which regulates the pressure in their cylinder chambers. The associated roll is mounted in bearings which are acted upon by variable forces to urge the associated roll toward the peripheral surface of the deformable shell. The forces acting upon the bearings for the associated roll determine the magnitude of stresses acting upon a web of flexible material in the nip between the two rolls. These forces are taken up by the bearings for the end portions of the deformable shell as well as by the hydrostatic supporting elements in the interior of the shell. It has been found that the patented roll assembly does not allow for a highly predictable (e.g., uniform) distribution of stresses in the longitudinal direction of the nip. This is due to the fact that the end portions of the shell are mounted on discrete bearings which, in turn, are mounted on the adjacent portions of the rigid and fixedly installed carrier for the shell. The bearings for the end portions of the shell prevent radial displacements of such end portions and they so prevent the intermediate portion of the shell from changing its shape in exact accordance with signals which are transmitted to the motors for the supporting elements in the interior of the shell.
German Auslegeschrift No. 10 26 609 discloses the possibility of mounting the bearings for the end portions of the deformable shell in such a way that the bearings are movable radially relative to the adjacent portions of the carrier. This solution is satisfactory as long as the bearings are actually free to move radially of the carrier. However, if the bearings happen to jam (e.g., if the radially extending guides for such bearings are out of commission), it is necessary to exert rather pronounced forces in order to shift the bearings radially of the carrier with the result that the purose of radial movability of the bearings is defeated and the deformable shell cannot assume an optimum shape for the treatment of webs or sheets of paper or the like.
German Offenlegungsschrift No. 28 18 011 discloses a roll assembly wherein two neighboring rolls are supposed to automatically define between themselves a clearance or gap of constant width. Each of these rolls is acted upon by a roll having a deformable shell through the medium of an intermediate roll. The bearings for the end portions of the deformable shells are adjustable in the radial direction of the respective carriers, and the hydrostatic supporting elements in the deformable shells are assembled into two groups. The supporting elements of each group can be shifted by adjustable fluid-operated motors and the bearings for the end portions of the shells carry pairs of sensors which are disposed diametrically opposite each other. The pressure of fluid which is admitted to the adjustable motors for the supporting elements is regulated in such a way that the end portions of the intermediate rolls are not stressed. This enables the two neighboring rolls of the roll assembly to establish and maintain between themselves a gap of preselected constant width. It has been found that the just discussed proposal is not entirely satisfactory because the forces acting upon the material to be treated cannot be regulated with a requisite degree of accuracy.